The volume control is a common point of failure and would affect all inputs and outputs. Could you open the pot and clean it? Sometimes turning it vigorously helps for a while :)
If you are used to electronics and have a few hours it's relatively easy to open up the pot and clean the carbon wipers. The short term fix tends to stop working after a while. I guess you could sell it while it works but there's a chance the new owner would receive it not fully working.
The volume control is a common point of failure and would affect all inputs and outputs. Could you open the pot and clean it? Sometimes turning it vigorously helps for a while :)